My son's 400 failed emissions 3 times last Saturday. We fiddled and fiddled and could never get the HC below 600 at idle. Max is 450. CO is .7,,,,way too lean, but the mix screws don't have any affect since he built this engine.

First pass the HC was 740 and CO was .3. We backed out the mix screws another 2 turns and backed the timing back to 14 at idle and got the HC down to the 600 and CO came up to .7, but its basically in a lean roll the whole time its idleing in gear.

The cam is the Comp roller 286 and World cast heads. Idle vacuum in drive is barely 8" due to the overlap.
To keep it running, I have the base idle screw cranked in pretty good compaired to where it was when I ran the carb on my 350 after going through it. Now the primary plates are open too far to engage the idle circuit.

Question its, how big and where do I need to drill the hole in each primany throttle blade so I can get the blades back down closer to the idle slot and get some idle mix back? I previously drilled the idle tubes and transition tubes so I know I have the capacity for more idle mix, just can't get the primary blades to close far enough and stay running.

Its already 2 months expired and he's dragging his feet on fixing it, so I guess its dads job!!! LOL